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Quantitative Chemical Analysis ACCURATE ACCURATE NOT Accurate PRECISE NOT precise PRECISE Random error systematic error Required math skills: • Add • Subtract • Multiply • Divide • Powers • Logarithms • Orders of magnitude • Estimation • Units • Conversions • Powers of 10 • Prefixes • Errors • Statistics Estimation and orders of magnitude: How many piano tuners are there in Chicago? Estimation and orders of magnitude: What is the national debt? Estimation and orders of magnitude: What is the world population? Estimation and orders of magnitude: How many water molecules in 1000 droplets? Estimation and orders of magnitude: A cube – 1” on a side (2.6)3 cm3 ~ 18 cc 1g 18 cc = 18 cc 18 g 1 cc N molecules 18 g = 18 g 6.022 x 1023 molecules 18 g Estimation and orders of magnitude: powers of 10 Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses A sample of NaNO3 weighing 8.50 grams is placed in a 500. ml volumetric flask and distilled water was added to the mark on the neck of the flask. Calculate the Molarity of the resulting solution. A sample of NaNO3 weighing 8.50 grams is placed in a 500. ml volumetric flask and distilled water was added to the mark on the neck of the flask. Calculate the Molarity of the resulting solution. 1. Convert the given grams of solute to moles of solute : 1 mole NaNO3 8.50 g NaNO3 0.100 mole NaNO3 85 g NaNO3 2. Convert given ml of solution to liters 1 liter 500. ml 0.500 liter 1000 ml 3. Apply the definition for Molarity: Molarity = moles NaNO3 / volume of the solution in liters 0.100 mole Concentration 0.100 M 0.500 liter Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses Determine the molality of 3000. grams of solution containing 37.3 grams of Potassium Chloride KCl. 1. Convert grams KCl to moles KCl 1 mole KCl 37.3 g KCl 0.500 mole KCl 74.6 g KCl 2. Determine the mass of pure solvent from the given grams of solution and solute Determine the molality of 3000. grams of solution containing 37.3 grams of Potassium Chloride KCl. 1. Convert grams KCl to moles KCl 1 mole KCl 37.3 g KCl 0.500 mole KCl 74.6 g KCl 2. Determine the mass of pure solvent from the given grams of solution and solute Total grams = 3000 grams = Mass of solute + Mass of solvent Mass of pure solvent = (3000 - 37.3) gram = 2962.7 gram . 3. Convert grams of solvent to kilograms 1 kg 2962.7 grams solvent 2.9627 kg 1000 grams 4. Apply the definition for molality 0.500 moles concentration 0.169 m 2.9627 kg Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses Determine the mole fraction of KCl in 3000. grams of solution containing 37.3 grams of Potassium Chloride KCl. 1. Convert grams KCl to moles KCl 1 mole KCl 37.3 g KCl 0.500 mole KCl 74.6 g KCl 2. Determine the mass of pure solvent from the given grams of solution and solute Determine the molality of 3000. grams of solution containing 37.3 grams of Potassium Chloride KCl. 1. Convert grams KCl to moles KCl 1 mole KCl 37.3 g KCl 0.500 mole KCl 74.6 g KCl 2. Determine the mass of pure solvent from the given grams of solution and solute Total grams = 3000 grams = Mass of solute + Mass of solvent Mass of pure solvent = (3000 - 37.3) gram = 2962.7 gram 3. Convert grams of solvent H2O to mols 1 mol 2962.7 grams water 164.6 mols H 2O 18.0 grams 4. Apply the definition for mole fraction mole fraction = moles of KCl 0.5100 =0.00303 total moles of KCl + water 0.500 164.6 Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses Determine the mass % of a NaCl solution if 58.5 grams of NaCl was dissolved in 50 ml of water (assume the density of water to be 1 g/ml) 1. Convert ml of water to grams 1g 50 ml 50 grams water 1 ml 2. Determine total mass of solution Mass of solution = mass of solute + mass of solvent = 58.5 + 50 = 108.5 g 3. Apply the definition of mass percent mass % = 58.5 (100) / 108.5 = 53.9% NaCl Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction = Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses Assuming the density of water to be 1 g/mL we approximate the density of a dilute aqueous solution to be 1 g/mL 1 g 1 ppm = 1g 1 g 1 g 1 g 1 g 1 ml 1 ml 1 ppm = 1 μg/mL = 1 mg/L 1 ppb = 1 ng/mL = 1 μg/L Determine the ppm of a NaCl solution if 58.5 grams of NaCl was dissolved in 50.0 ml of water (assume the density of water to be 1 g/ml) Convert ml of water to grams 1g 50 ml 50 grams water 1 ml Determine total mass of solution Mass of solution = mass of solute + mass of solvent = 58.5 + 50.0 = 108.5 g Apply the definition of ppm 58.5 (106) / 108.5 = 5.39 x 105 ppm NaCl

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